Renal autoregulation of arterial blood pressure requires maintenance of plasma and extracellular fluid volumes. Two mechanisms are thought to be involved in renal autoregulation: the tubuloglomerular feedback (TGF) and a vascular myogenic mechanism (VMM). The objective of this project has been to characterize the dynamics of these autoregulation mechanisms by using induced broadband perturbations of arterial pressure and nonlinear modeling methodologies. Comparisons of nonlinear models of renal blood pressure and flow data obtained for normotensive rats and spontaneously hypertensive rats, based on the novel apporoach of ``principal dynamic modes'', show unambiguously that the relative effect of the TGF mechanism is diminished in hypertensive rats. This finding advances our understanding of hypertension and may lead to more effective clinical treatments.